Unpredicted CT string failures have not completely disappeared despite the industry having a greater understanding of cycle fatigue. A comprehensive process to systematically analyze CT string failures (field-based) has been in place since 1995. This system is described and details of a CT string failure database discussed. The database includes over 120 entries from the period 1995 through 1998 derived from worldwide CT operations of Schlumberger Dowell. The process delivers two principal data sets: the mode of failure (failure mechanism) and the cause (failure cause).

The four-year study period enables failure trends to be identified. Such trends are evident in both in failure mechanism and cause and are discussed.

Evaluating the "expired life" of the CT strings under study has led to the conclusion that traditional and current string management procedures (that are based on low cycle fatigue accumulation) are inadequate. This has implications in both the prediction of CT string failure and the optimization of string use.

The CT string failure data is derived from CT operations conducted by over 150 CT units that completed in excess of 35,000 operations during the study period. The volume of tubing used during these operations, in combination with the accumulated failures, allows for the introduction and discussion of "Tubing Performance Indicators", which the author believes can be considered representative for the industry.

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